The invention relates generally to a method and apparatus for the study of the motion of the human body. In particular, the invention relates to a method and apparatus for videofluoroscopic analysis of joint motion which is recorded and compared to a reference recording of previous or desired joint motion.
Since the 1920s, fluoroscopic examinations have been recorded, first on film by a technique known as cineradiography. The ability to record fluoroscopic examinations permitted a means for storage of the exam. This permanent record of the exam could be analyzed at a later date and replayed as many times as necessary at a variety of speeds. The widespread availability of video recording systems in the late 1970s and 1980s has led to the replacement of cineradiography with videofluoroscopy, the process of videotaping a fluoroscopic study for playback on a video cassette recorder. However, there is little use of videofluoroscopy as it relates to the skeletal system. Historically, the primary applications of fluoroscopy have been for study of the gastrointestinal tract, the pulmonary and cardiovascular systems and in myelographic and arthrographic examinations, those systems and studies where organ or fluid movement must be seen if accurate diagnosis is to result. The traditional method of imaging the musculoskeletal system has been, and remains, standard radiographs. The benefits of using fluoroscopy for skeletal analysis has not been widely recognized. Static x-rays simply cannot reveal the same kind of information that dynamic studies provide.
Interest in fluoroscopy has been replaced by interest in computerized imaging techniques. In the 1970s, computed tomography (CT) scanners demanded the radiologists attention, followed by the development of nuclear magnetic resonance (NMR) systems. A new method of skeletal analysis also developed in the 1970s: computer modeling. In this process, the biomechanical functioning of the spine is studied through mathematical analysis, often including model projections, some of which are three-dimensional.
The 1980s have seen a return to interest in fluoroscopy studies. However, the focus of attention now rests on the hook-up of the fluoroscope to the computer, not its hook-up to a video system. Called digital fluoroscopy (or digital radiography or subtraction imaging), this technique subtracts one fluoroscopic image from a later one. The process involves complex computer circuitry and programming and, like CT and NMR scanners, the cost of equipment and complexity of technology limit its availability primarily to hospitals. Thus far, the major application of digital fluoroscopy has been in the study of the cardiovascular system, with bony structures subtracted from the images. Recent developments in medical imaging involve the construction of three-dimensional pictures by computer.
Cine studies of the skeletal system were first reported in the 1950s. This early work was confined to examinations of the cervical spine and consisted primarily of attempts to determine normal and abnormal neck movement. Many reports on the use of cineradiography to study and define joint motion appear in the literature. Numerous joint motion studies using cine have been carried out by doctors of chiropractic. It seems that the chiropractic profession is doing more to fine tune the videofluoroscopic technique than anyone else, partly because chiropractors do not have easy access to other imaging tools such as CTs and NMRs and partly because their profession is more concerned with joint motion, i.e., determining what exactly happens when a joint moves.
James Mertz briefly discussed videofluoroscopic studies of the cervical and lumbar spine (ACA Journal of Chiropractic, pages 74-75). Increased ranges of motion most often resulted from injury to the retaining ligaments, while restricted ranges of motion resulted from structural asymmetry, degenerative changes, and muscular imbalances. He observed that stretched ligaments heal by scar formation, but they can no longer maintain relationships of adjacent bone structures; in contrast, muscles may alter the range of motion of bone structures, but they do not affect relationships. Stress patterns (of altered joint motion or relationship) result in joint degeneration; by using videofluoroscopy to evaluate spinal motion, degeneration resulting from hypermobility and hypomobility can be predicted. Although some text books on skeletal disorders point to the usefulness of fluoroscopy, its widespread use as a diagnostic procedure on skeletal disorders is not widely recognized. In general, fluoroscopy is utilized most often for the study of systems other than the musculoskeletal system, primarily the cardiovascular system (i e., angiograms) and the gastrointestinal tract (i.e., upper and lower GI barium studies).
Mintz, et al. (American Journal of Cardiology, 1980, 45/2, pages 210-216) discussed an experimental use of videofluoroscopy to study patients undergoing coronary arterial bypass graft surgery. To evaluate left ventricular performance and segmental wall motion, radiopaque tantalum markers were implanted into the left ventricular wall during bypass surgery. Postoperatively, fluoroscopic images were recorded on a video disc recorder and replayed frame by frame. The authors then digitized the images for computer analysis, using a light pen to mark the X and Y coordinates of the implanted marker positions during three successive cardiac cycles. These coordinates were related temporally to the R wave of the analog electrocardiographic signal, recorded as a horizontal bar on the video image. Each measurement was averaged and statistical differences were assessed.
Chiropractors seem to be more involved in the development of the videofluoroscopic technology than other physicians. For example, two research projects, both in Europe, have attempted to measure objectively the motion observed on cineradiographic exams. In general, such projects have employed faulty or weak methodology in trying to elicit objective measurements from moving pictures.
In 1979, Masters and Sugiyama (thesis for Anglo-European College of Chiropractic) reported on the use of cineradiology for measurement of range of movement, roll, and shear of each vertebra between C2-C6. Range of motion was first measured by goniometer and plain films. The cine film was projected onto a screen covered with acetate sheets, where the axes of vertebra were drawn from the projected film for frame-by-frame analysis. They then plotted fourteen different ranges of measurement for each 1/25 of a second onto a graph to detect motions not observable when cine films were run at normal speed. When film was viewed as a moving picture, a fan-like movement of the vertebra was seen. On the other hand, when analyzed frame by frame, graphs indicated that movement really consisted of a ragged see-saw progression as the neck moved. In shear movement, for example, one intersegment appeared to remain static while the rest showed a rocking motion; as the neck moved, another interspace took over this static roll and the previous one rocked on its axis.
Work by Gideon Ariel has focused on computer analysis of biomechanical data and particularly studying athletic performance and making suggestions for improvements. His method involved filming athletes participating in throwing events by high-speed motion picture camera set at a 90.degree. angle to the athlete's sagittal plane. After being projected upon a translucent glass screen, the film was digitized with a sonic stylus, and the X and Y coordinates were stored in a computer's memory. As each frame was digitized, joint centers were projected onto a graphic display screen and connected by lines to form stick figures. Computer analysis calculated parameters such as total body center of gravity, segment velocities and accelerations, joint forces and movements of force.
Two other types of fluoroscopic imaging are known. Dynamic radiography, developed in 1974, is a noninvasive technique utilizing scatter radiation rather than direct transmitted radiation to monitor and measure myocardial mechanics during fluoroscopy. Another technique relates to the photokymograph (PKG), a noninvasive instrument for recording segmental myocardial wall motion from self-illuminated images, such as those produced by fluoroscopy, cine ventriculography, two dimensional sonography, and scintigraphy. As with all the other prior art discussed above, these fluoroscopic imaging techniques are unable to provide an objective comparative analysis of joint motion.